A fun LJ meme: casting various traditionally white comic-book characters as actors of color. There's a good starting point at Fantastic Fangirls, with some examples (my favorite of which is Vanessa Williams as Emma Frost, the White Queen [added later: that one's from bossymarmalade's list]) and links.
Another specific suggestion I like, from liviapenn: D.B. Woodside (Principal Wood from Buffy) as Tony Stark.
The meme has gone beyond comics, too—for example, there's a suggested all-PoC cast for Buffy. I especially like the idea of Gabrielle Union as Buffy and Percy Daggs III (Wallace from Veronica Mars) as Xander.
And then there's the all-female Star Trek reboot recasting, which goes a little far afield from the idea of using living actors in some cases, but I love the idea of Indira Gandhi as Sarek. (And though I'm not familiar with Judith Scott, the photo of her on that page does seem to me to capture rather more of Spock's look than, say, Zachary Quinto's perpetual semi-smirk does.)